| 1. |
- Eliasson, Lena, et al.
(författare)
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PKC-dependent stimulation of exocytosis by sulfonylureas in pancreatic beta cells
- 1996
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 271:5250, s. 813-815
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Tidskriftsartikel (refereegranskat)abstract
- Hypoglycemic sulfonylureas represent a group of clinically useful antidiabetic compounds that stimulate insulin secretion from pancreatic beta cells. The molecular mechanisms involved are not fully understood but are believed to involve inhibition of potassium channels sensitive to adenosine triphosphate (KATP channels) in the beta cell membrane, causing membrane depolarization, calcium influx, and activation of the secretory machinery. In addition to these effects, sulfonylureas also promoted exocytosis by direct interaction with the secretory machinery not involving closure of the plasma membrane KATP channels. This effect was dependent on protein kinase C (PKC) and was observed at therapeutic concentrations of sulfonylureas, which suggests that it contributes to their hypoglycemic action in diabetics.
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| 2. |
- Gromada, Jesper, et al.
(författare)
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CaM kinase II-dependent mobilization of secretory granules underlies acetylcholine-induced stimulation of exocytosis in mouse pancreatic B-cells
- 1999
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Ingår i: Journal of Physiology. - 1469-7793. ; 518:3, s. 745-759
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Tidskriftsartikel (refereegranskat)abstract
- 1. Measurements of cell capacitance were used to investigate the mechanisms by which acetylcholine (ACh) stimulates Ca2+-induced exocytosis in single insulin-secreting mouse pancreatic B-cells. 2. ACh (250 microM) increased exocytotic responses elicited by voltage-clamp depolarizations 2.3-fold. This effect was mediated by activation of muscarinic receptors and dependent on elevation of the cytoplasmic Ca2+ concentration ([Ca2+]i) attributable to mobilization of Ca2+ from intracellular stores. The latter action involved interference with the buffering of [Ca2+]i and the time constant (tau) for the recovery of [Ca2+]i following a voltage-clamp depolarization increased 5-fold. As a result, Ca2+ was present at concentrations sufficient to promote the replenishment of the readily releasable pool of granules (RRP; > 0.2 microM) for much longer periods in the presence than in the absence of the agonist. 3. The effect of Ca2+ on exocytosis was mediated by activation of CaM kinase II, but not protein kinase C, and involved both an increased size of the RRP from 40 to 140 granules and a decrease in tau for the refilling of the RRP from 31 to 19 s. 4. Collectively, the effects of ACh on the RRP and tau result in a > 10-fold stimulation of the rate at which granules are supplied for release.
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| 3. |
- Lebrun, Philippe, et al.
(författare)
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Dynamics of the cationic, bioelectrical and secretory responses to formycin A in pancreatic islet cells
- 1996
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Ingår i: Pflügers Archiv. - 0031-6768. ; 431:3, s. 353-362
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of the cationic, bioelectrical and secretory responses to formycin A were monitored in pancreatic islet cells in order to assess whether this adenosine analogue, which is known to be converted to formycin A 5'-triphosphate in isolated islets, triggers the same sequence of ionic events as that otherwise involved in the process of nutrient-stimulated insulin release and currently attributed to an increase in adenosine 5'-triphosphate (ATP) generation rate. Unexpectedly, formycin A first increased 86Rb outflow, decreased 45Ca outflow and inhibited insulin release from prelabelled islets perifused at physiological or higher concentrations of D-glucose. This early inhibitory effect of formycin A upon insulin release coincided, in perforated patch whole-cell recordings, with an initial transient increase of ATP-sensitive K+ channel activity. A positive secretory response to formycin A, still not associated with any decrease in K+ conductance, was only observed either immediately after formycin A administration to islets already exposed to glibenclamide or during prolonged exposure to the adenosine analogue. This coincided with an increase of cytosolic Ca2+ concentration in intact B-cells and a greater increase of membrane capacitance in response to depolarization in B-cells examined in the perforated patch whole-cell configuration. The latter stimulation of exocytotic activity could not be attributed, however, to any increase in peak or integrated Ca2+ current. Thus, the mode of action of formycin A, or its 5'-triphosphate ester, in islet cells obviously differs from that currently ascribed to endogenous ATP in the process of nutrient-stimulated insulin release.
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